1. Field of the Invention
The present invention relates to a scribing method for forming scribe lines on a brittle plate such as a glass plate, a semiconductor wafer, or a ceramic plate, to a cutter wheel used for such a method by rotating the wheel on a brittle sheet; and to an apparatus provided with such a cutter wheel.
2. Description of the Prior Art
A cutter wheel for brittle materials is fabricated by working a disk made of a cemented carbide alloy, sintered diamond or the like. The disk is ground at the outer periphery obliquely on the two sides to form an edge having a V-shape. A rotational shaft is fixed to a shaft hole provided at the center of the disk, and the shaft is rotatably mounted in a manual cutter or in a cutter head of an automatic scriber or the like. Accordingly, the cutter wheel is rotated on a brittle plate such as a glass sheet, a semiconductor wafer or a ceramic plate under a pressure to form scribe lines on the brittle plate.
However, such a conventional cutter wheel cannot generate deep vertical cracks inside a brittle sheet. Further, the wheel is liable to slip on a brittle sheet during scribing, and this abrades the edge. In addition, residual stress remains along scribe lines. Further, when the brittle sheet is cut along the scribe lines, unnecessary defects due to horizontal cracks are liable to be generated at the sections subjected to the cutting. This is a problem concerning the quality of brittle cutting.
Deep vertical cracks can be obtained by the cutter wheel disclosed in the U.S. Pat. No. 5,836,229. As shown in FIG. 1, the cutter wheel 1 has a disk with V-shaped bevel portions 2, and an edge 3 between the bevel portions 2 has depressions 4 of microscopic sizes spaced apart at equal distances to provide protrusions 5 between them which contact a brittle sheet. It is possible by use of the cutter wheel 1 to generate deep vertical cracks into a brittle sheet. Further, the residual stress is decreased, and the generation of unnecessary defects due to horizontal cracks along the scribe lines is not increased.
One of the main uses of the cutter wheel for brittle materials is cutting of glass sheets used for flat panel displays (FPD""s for abbreviation) such as liquid crystal display (LCD for abbreviation) panels. Recently, there is a high demand for LCD panels of high quality. Therefore, it is necessary to suppress the generation of unnecessary horizontal cracks as much as possible.
An object of the present invention is to provide a scribing method for brittle materials which generates deep vertical cracks while also suppressing generation of horizontal cracks.
Another object of the present invention is to provide a cutter wheel for brittle materials which generates deep vertical cracks while suppressing generation of unnecessary horizontal cracks.
A further object of the present invention is to provide a scribing apparatus which suppresses generation of horizontal cracks by using the cutter wheel as a scribing means.
A cutter wheel for brittle materials in accordance with the present invention comprises a disk with two side planes and an outer peripheral portion between the planes. The outer peripheral portion has two bevel portions, and there is a ridge portion having a polygon shape between the bevel portions. The ridge portion comprises a plurality of peaks aligned along a circumferential line. For each pair of two adjacent peaks in the plurality of peaks, the ridge portion except the peaks extends along (or lower than) a straight line connecting the two adjacent peaks. Preferably, the peaks are arranged an equal distance apart. For example, for each pair of two adjacent peaks, the ridge portion has a polygon shape with vertices along the straight line connecting the two adjacent peaks. Thus, the edge portion has a polygon shape. Alternatively, for each pair of two adjacent peaks, the ridge portion has a depression between the two adjacent peaks, and the depression extends lower than the straight line connecting the two adjacent peaks.
An advantage of the present invention is that generation of horizontal cracks is remarkably suppressed while generating deep vertical cracks.